Television transmitting system



Patented Mn. 21, 1944 UNITED STATES PATENT orrlcs muses TELEVISION mausmr'rmosrs'rm Alfred N. Goldsmith, New York, N. Y. Application May 29,1942, Serial No. 444.965

9 Claims. (01. 88-163) This invention relates to an improvement in-television transmitters, and more particularly 'to transmitters whereinthe subject matter is derived from'a moving'picture film.

In the transmission of-television programs it is frequently desirable ornecessary to derive some of the material transmitted from a motionpicture film, particularly where the subject matter is difiicult toderive from the television studio or,

for example, under conditions where the action transpired some timepreviously and was recorded on a standard film. If the film frame speedof, the film bearing the "subject matter to be transmitted were exactlythe same asthe television fleld or framefrequency, transmission ofsubject matter from moving picture film would be greatly simplified.This condition does not exist undertlie present "andards of motionpicture recording and television picture ti'ansmis-- sion. Standard 35mmiymovingpicture film is generally photographed and projected at therate of 24 frames per second, whereas standard black and w te televisionprograms are transmitted at the ra of 60 fields persecond interlaced'soas to form 30 frames per second. Naturally, the ap- 2.

parent movement would be accelerated to a point where it would seemunnatural if the moving picture film were projected at a rate of 30frames per second and the accompanying sound as"recorded on the filmwould be unacceptably raised in pitch, so that some means is necessaryto permit the moving picture projector to operate at 24 frames persecond, while the-television transmitting system operates at 30 framesper second. Various methods have been devised for permitting thisoperation/one method .being the use-of an intermittent projector inwhich alternate frames supply two television images for two successivetelevision fields, whereas the remaining film frames supply threetelevision images for three television fields. An example of such asystem and apparatus is shown and described in Bed ford Patent No.2,227,054, issued December 31,

1940, and a different system is shown and described in" Seeleyapplication Serial No. 291,309. 45.

filed August-22, 1939. The use of intermittent projectors, however, isnot wholly satisfactory when used with television pick-up tubes of thenon-storage type and when pick-up tubes of that ously so that the rateof movement of the film through the projector is uniform and thefilm isnot moved intermittently. However, when continuous projector-s areemployed, naturally the projector must also include some type of imagerectification. The image rectifier performs the function of causing theimages of the individual film frames to be projected in a stationarymanner upon a screen electrode or surface. This is accomplished eventhough the film moves continuously at a constant rate of speed, and insuch lenses being so locatedas to perform the desired imagerectification. Still another form of image rectifier that is knownin theprior art is in the form of. a. rocking or oscillating mirror, whichcruises the moving images to be projectedin stationary'manner upon aprojection screen. Still other types of image rectifiers use rotating oroscillating plates on polygonal prisms. Various types of imagerectifiers to be used with continuous moving picture film projectorsare, for example; shown and described in the United States patents toMechau, No. 1,543,224, issued June 23, 1925; No. 1,584,317, issued May11, 1926; and No. 1,893,374, issued January 3, 1933.

In the described types of continuous or non- 'intermittent variablebrightness projection the film is advanced at a uniform velocity throughthe film gate of the projector. At least parts of at least two filmframes are within the illuminated portion of the image projection systemat all times, and by one of the above referred to optical rectirlersimages of successive frames are projected in superposition and theefiects of film type are used it.is desirable to employ a con- 50tinuous film projector. The use of a continuous film projector-alsoaifords other inherent advantages.

It is therefore desirable to be able to motion are neutralized; Further.the optical arrangemnts are such that as one film frame is faded out thenext film frame is gradually brought .in. Unfortunately, however-An thistype of projection the fading. out of one film at any given point of thefield does not occur at the same rate as the bringing in of the nextpicture at the same part ofthe fi'eld. Thus,.there are inherently ovingpicture projectors that operate continu- 66 b lhtnesi variations at allparts of the field or 2 2,s44,eos

object area throughout the projection cycle, and the law governing theamplitude variation and phase 01 the illumination cycle varies from onepart of the field to another. In general, these variations in brightnessare considerably less than 100%. However, in all presently knowncontinuous projectors wherein image rectifiers are used, the variationsare finite and usually of sufficient magnitude to be noticeable,particularly in those portlons'toward the edge of the picture wherevignetting effects during the cycle or other optical eflects conspire toproduce maximum brightness variations. Regardless of the particuis! typeof optical rectification used, whether it be mirrors, polygonal glassprisms, plates, lens wheels or drums, some variation in averagebrightness is present, and it is highly desirable that this variation inbrightness (irrespective, of course, of changes in the picture contentitself) be eliminated to reduce the apparent flicker in the producedtelevision image.

One purpose of the present invention, therefore, resides in theprovision of means whereby brightness variations in the projected imagefrom a continuous film projector may be compensated for to remove theeffects of the brightness variations on the screen or area upon whichthe images are projected.

Another purpose oi the present invention resides in the provision of anapparatus operated in synchronism with the continuous projector for tingfor changes in the average brightness oi the projected image, as well asbrightness changes in each part thereof, to eliminate there- 7 byflicker effects on the screen that would otherwise be apparent when acontinuous film projector and image rectifier is employed.

-A still further purpose 0! the present invention resides in theprovision 01 a cyclically variable translucent filter device interposedin the optical axis of a continuous film projector and image rectifierto eliminate the inherent brightness variations in any and all parts ofthe field that are associated with the usualoperation results from acontinuous projector.

Still another purpose ot-the present invention resides in the use of acontinuous film projector and image rectifier tor projecting film imagesonto a light responsive electrode in a television transmitting tube,together with means interposed in the optical path for compensating forthe inherent brightness variations associated with continuous filmprojectors, whereby substantially flickerless television images may beproduced at a television receiver.

Various other purp ses and advantages of the present invention willbecome apparent to those skilled in the art from the following detaileddescription, particularly when considered in connection with thedrawing, wherein:

Figure 1 represents a portion of a television transmitting system.

, a. focused cathode ray beam, and a deflection yoke 25 for causinghorizontal and vertical deflection of the cathode ray beam in order thatthe mosaic or light responsive electrode it may be scanned by th cathoderay beam. In order to perform the scanning operation horizontaldeflection voltage variations may be applied to the terminals 28, whilevertical deflection voltage variations may be applied to the terminals30 in order that the deflection yoke 25 may produce the desired andnecessary electromagnetic field. The picture signals developed by thescanning operation are applied across the output load resistance 32 oithe transmitting tube, and these same picture signals are available fromthe output terminals 34 by way of coupling condenser 36. The picturesignals as derived from the output terminals 34v may then be subjectedto the desired amplification in order that their intensity may beincreased, and thereafter synchronizing signal and blanking signals maybe added in a manner well known in the prior art, so that the resultantcomposite series of signals may then be used to modulate a radiofrequency carrier.

For driving the continuous projector a motor II is provided which ismechanically coupled to the driving shaft 40 of the continuousprojector. This motor operates the projector at a rate such that thefilm will be transported through the projector at a rate ofapproximately 24 film frames per second in orderthat the proper apparentmotion will be attributed to the subject matter contained on the film.

In the system as so far described optical images will be projected onthe light responsive electrode ll of the television transmitting tube,but these optical images will vary in brightness irrespective of thepicture content of th film, the variations occurring in synchronism withthe operation or the continuous projector, and particularly insynchronism with the image rectifier associated therewith. In somecontinuous projectors and image rectifiers this variation in brightnessmay be as much as 40% at some particular portions of the image area.

There are shown in Figure 2 of the drawing three curves representing thevariation in brightness at three particular portions of the image area.The solid line curve might, for example, represent the variation inbrightness at the top of the picture, in which case the brightness woulddiminish quite rapidly after the beginning of one film irame cycle, thenincrease gradual y to a maximum at the termination of each film framecycle. The curve represented by the dot and dash line might, forexample, represent the light intensity at thecenter oi the picture, andat this portion or the picture there might be no variation inbrightness, in which case the curve is represented as a horizontal lineat approximately brilliance (disregarding picture content). As a thirdexample, a dotted line is shown in Figure 2 representing. for example.

the variations in brightness at the bottom of the picture. Associatedwith the curve is shown the distance represented by one film frame inpoint of time.

In order to compensate for these variations in brightness a disc 50 isprovided, which is preferably located at the plane 20 of the aerialimage. This disc is driven by shaft 52, which in turn is connecteddirectly or by means of appropriate gearing to the driving motor 38.Inasmuch as the disc 50 and the continuous projector in are both drivenby the motor 38, they necessarily operate in synchronism and in properphase with each other.

In order to compensate for the undesired brightness variationsintroduced by reason of the image rectifier the periphery of the disc 50is so constructed as to have varying light transmitting qualities. Inorder that the variations in brightness may be compensated for, thetransparency of the peripheral turn of the disc is made such that lightwill be absorbed by the disc in inverse relation to the brightnessvariation at all parts of the optical image. In other words, all partsof the image projected on the screen electrode H of the televisiontransmitting tube are reduced to correspond to the lowest. yet finite,intensity of any portion of the optical image. The equalizer disc. 5G,therefore, may well be in the form of a variable density, movable filtercovering the entire aerial image area 20, and having at all points andat all times a density or light absorption capacity such that itneutralizes all brightnesses of the image above a fixed minimum or datumamount. Thus, it

thedarkest part of the aerial image at any time has a brightness of, say60% of the maximum brightness, then the density or absorption of theequalizer at that part oi'the image and at that instant for the darkestpart of the picture must be zero, while the density or absorption of thefilter of the brightest part of the picture at the corresponding timemust be such that 40%. of the light is absorbed, thus equalizing thepicture brightness. It is also necessary that the equalizer or filterdisc 50 be moved relative to the aerial image in such fashion that it issynchronized with the brightness variations thereof, which is readilyand conveniently accomplished by directly connecting the equalizing disc58 to the motor 38 that drives the continuous projector. The equalizerdisc 50 may make one revolution for each cycle of operation of the imagerectifier, or a single revolution of the equalizer disc may represent aplurality of integer cycles of operation of the image rectifier. If theequalizing disc Ell makes one revolution per rectification cycle, thedensity band thereon, which will be circular, must correspond to onerectiilcatlcn cycle. If the equalizer makes one half revolution perrectification cyclc,'the density band thereon must correspond to tworectification cycles, etc. Figure 3 shows a series of three curves representing the transparency of particular portions of the equalizer disc50 as related to the corresponding portions of the image and thebrightness variations represented by the curves shown in Figure 2. Thesolid line curve of Figure 3, therefore, corresponds to the variation intransparency as a function of time for exactly compensating forbrightness variations in the top of the picture when the variation inlight is such as that represented by the solid line curve Gil shown inFigure 2. The dot and dash line and the dotted line of Figure 3similarly correspond to the similarly represented curves in Figure 2. InFigure 4 there is shown a portion of the periphery of the equalizer disc50, the density band, however, being shown straight rather thancurvedfor the sake of clarity. One cycle of the density band isindicated in Figure 4, and by comparing the curves shown in Figure 3with the density at the top, center, and bottom of the density band, therelationship is at ondf. apparent.

When an equalizer disc 50, having the proper variation 'in density orlight absorption, is used with a continuous film projector and imagerectifier, all variations inbrightness as a result of the operation ofthe image rectifier may be completely compensated for. When this is thecase any relationship of film frame and television frame frequency maybe present, and the television pictures may be transmitted at anyparticular desired frequency irrespectiveof the speed of operation ofthe continuous projector. The variations in brightness of the imagesprojected by the, continuous projector, disregarding subject mattercontained on the film, is entirely a function of the operation of theimage rectifier associated with the projector, and once the properdensity band has been determined, that density band will exactly correctfor light intensity variations for theparticular image recti-' fier. Itis not necessary to alter the equalizer disc 50 in any way when the filmis changed in the projector, or when the subject matter contained on thefilm is altered. In accordance with this invention the equalizer discmay be used with any type of continuous projector regardless of the typeof image rectification em-- ployed.

There are various methods by which an equalizer disc may be made whichwill exactly match the inherent brightness variations for a. particularimage rectifier. One of these methods is to employ an unexposedphotographic plate of optical glass coated with an emulsion of very finegrain. This photographic plate, which pref erably could be in the formof a disc such as shown at 50 in Figure l, is positioned in the normaloperating position of the equalizer disc,

and the projector is operated for one or more cycles, during which timethe disc is synchronously rotated through one revolution. This is donewith a blank field or completely transparent film in the projector.Naturally, no extraneous light is permitted to strike the plate, theonly light permitted to fall on the photographic plate being that of theaerial image produced by the continuous projector per se. The plate,after exposure, is then removed and developed as a photographic negativeuntil its density or light transmission in all parts corresponds to thevalues required as set forth above. Such an equalizer made as aphotographic negative may then be cemented to a circular plate ofoptical glass so as to protect it from deterioration. The resultantequalizer will then exactly match the inherent light variations of .theassociated continuous projector.

It will also be possible to make an equalizer disc by actually measuringvariations in light intensity by a photometer or other equivalentapparatus, and subsequent to such measurements construct a variabletranslucency band whichy would have the desired light absorbingproperties and variations. Such a method, however, would be quitetedious and costly, particularly as compared with the method abovedescribed wherein an unexposed light sensitive film or plate isemployed.

It is not necessary that the equalizer disc 50 be in the form of a discas shown in Figure 1, since it is entirely feasible that the equalizercould be in the form of an endless film or band which could be movedthrough the aerial image plane 20. The equalizer disc or variabletranslucency band could also be constructed in various other manners.

Furthermore, in the system shown in Figure l, a conventional iconoscopeis shown. However, it is to be understood that various othertransmitting tubes such as the orthicon could as well be employed.

Various other alterations and modifications may be made in the presentinvention without departing from the spirit and scope, and it is desiredthat all such modifications be considered within the purview of thepresent invention except as limited by the herein appended claims.

What I claim is:

1. A continuous moving picture projector in cluding an image rectifyingsystem for producing substantially stationary images of the separatefilm frames, the operation of the continuous projector inherentlycausing undesired cyclic brightness variations in the produced images, alens system associated with the projector for producing an aerial imageof the subject matter contained on the film frames, an equalizer discpositioned substantially in the plane of the aerial image, means forrotating said disc in synchronism and in phase with the operation of thecontinuous projector and image rectifier, said equalizer disc beingprovided with a peripheral band of variable transparency, the variationsin transparency extending both radially and circumferentially andcorresponding to the undesired brightness variations of each portion ofthe image during each rectification cycle, and a further lens system forprojecting the aerial image onto an image receiving surface, whereby theimages projected on the surface will be free from objectionablevariations in picture brightness.

2. A continuous moving picture projector. in-

cluding an image rectifying system and a lens system for producingsubstantially stationary aerial images of the separate film frames ofthe continuously moving film, the operation of the continuous projectorinherently causing unequal undesired brightness variations in variousportions of the produced images, an equalizer disc having a portiqp ofits periphery positioned in the aerial image plane, said equalizer discbeing provided with a peripheral band of variable translucency, thetranslucency variations corresponding to the undesired brightnessvariations occurring in the various portions of the images during eachimage rectification cycle, means to rotate said disc in synchronism andin phase with the operation of the continuous projector and imagerectifier, and a further lens system for projecting the aerialimage ontoan image receiving screen, whereby the optical images projected on thescreen will be free from objectionable brightness variations.

3. A continuous moving picture projector including an image rectifyingdevice, a lens system qasfociated with the continuous projector forprosubstantially stationary aerial images of assaees the subject mattercontained on the film frames, the operation of the continuous projectorinherently causing undesired cyclic brightness variations in theproduced images, an equalizer disc positioned in the aerial image plane,means for rotating said disc in synchronism with the projector and inproper phase with the operation of the image rectifying device, saidequalizer disc being provided with a peripheral band of bidimensionallyvariable light transparency corresponding to the undesired cyclicvariations in brightness of all portions of the image occurring duringeach image rectification cycle, and a further lens system for projectingthe aerial image onto an image receiving surface, whereby the imagesprojected on the surface will be free from the undesired objectionablebrightness variations.

4. A continuous film projector including an image rectifier, lens meansfor producing aerial images at a predetermined image plane, means forfocusing the aerial images onto the light image receiving surface, saidcontinuous projector and image rectifier causing different undesiredcyclical variations in picture brilliance for different portions of eachimage rectification cycle, a brilliance correction disc positionedsubstantially in the plane of the aerial image, the periphery of saiddisc being provided with a variable density band chosen in accordancewith the undesired variable brilliance of the diife'rent portions of theimages during each rectification cycle, and means for rotating said discin synchronism and in proper phase relationship with the operation ofthe continuous projector and image rectifier, whereby the undesiredvariations in the brilliance of the images projected on the surface willbe eliminated.

5. A continuous film projector including an image rectifier, lens meansfor producing substantially stationary aerial images of the film framesat a predetermined plane, means for 10- cusing the aerial images onto a,light image receiving screen, said continuous projector and imagerectifier causing undesired cyclical variations in picture brillianceover substantially the entire image area during each image rectificationcycle, a brilliance correction device posi tioned substantially in theplane of the produced aerial images, said correction device beingprovided with a variable transparency band, the variations intransparency extending in substantially all directions throughout theeffective portion of the band and determined, in accordance with theundesired variable brilliance during each rectification cycle, and meansfor moving said device in synchronism with the projector and in properphase relationship with respect to the image rectifier, whereby theundesired variations in the brilliance of the images projected on thelight screen will be substantially eliminated.

6. An optical image projection system for use with a motion picture filmcomprising a continuous film projector including an image rectifier,lens means for producing substantially stationary aerial images of thefilm frames at a predetermined image plane, means for focusing theaerial images onto an image screen, said continuous projector and imagerectifier causing undesired cyclical variations in picture brillianceduring each image rectification cycle, a brilliance correction discpositioned substantially in said predetermined image plane, theperiphery of said 2.34m disc being provided with a. variable densityband having both radial and circumferential variations in density chosenin awordance with the unde- -aired variable brilliance oi. each portionor the image during each rectification cycle, and meansi'brrotatlngsaiddiacinandin proper phase relationship with the operationoi.

the continuous projector and image rectifier, whereby the undesiredvariations in the brilliance will be eliminated from the imagu proiectcdon the imageacreen.

7. A motion picture projecting system for pro-. jecting imagesoitheseparate irameooi'amcving' 'picturefllmoomprisingacontinuousproiectorincluding an image rectifier, means including alensaystemiorproducingoerialimageaotthemmiramea,afurtherlermaystemiortocusing the aerial images'onto an imagereceiving screen, said continuous projector and image rectifier infl y'Producing undesired cyclical variations in brilliance of the images, atranslucent equaluer member positioned substantially in the plane of theaerial images, said translucent equalisermembercyclicallyvarylngintranrlucencyinali directions over its effectivearea in acoo .with the cyclical variations in brilliance oi allportionaottheimagenandmeansiormoving said equalizing member through theoptical path ottheprojectorat theplaneoitheaerialimageainaynchronismandinphaaerriththeoperation Rent cyclical variations inbrightness ol -eachcent equalizer member positioned lathe aerial imageplane. said tIeql -lizer member having a portion thereofcyclicallyvarying in transparency in accordance with the undesired cyclicalvariations ill-brilliance of each portiono! the produced images, andmeans for moving the variable transparency portion of said equalizingmember through the optical. path attheaerialimageplaneiriwith the speedof operation oI-the projector and in phase with the operation 0! theimage rectifier to thereby eliminate the undesired time.

amoving' picture fllm comprising a continuous motionpicturefllmprojectorincludinganimage rectifying device; means including a lens system forproducing substantially stationary aenal image: ot'the film irameaatapredetermined planc,aiurtherlenssystemior iocuaingthe z'idal imagesontoan image receiving screen.

tionaoitheproducedmmlmflgefi'ighh inthesaidpredeterminedplaneaidequaliaer" member including a. cyclica.l1yvarying-,lighttranalucencyportiomthetranslucencyvaiiation belng'dcterminedlnaccordance with the diiierdiiierent portion of the optical imagea. and

mcana! movingth'evariahl'elight' portion aaidequalilingmemberthroughtheopticallightpothoithe'mleotoratflteaeflal imagerlaneinandhrproperpbaaewithtln operation oi the continuous Mr brilliance varia- 9. A motionpicture projecting 2 for projecting optical images of theaeparate framesoi continuous projector and image r ifying 3 device inherentlyproducing'dlilerent undesired cyclical brightness variations indiiierent por-

